Interface

Yes it is possible.

You can add an extra gridRowLayout() outside for a!forEach and use the sum() function on the respective column. 

Something like this you can build.

a!localVariables(
  local!gridData: a!map(
    col1: "",
    col2: "",
    col3: "",
    col4: "",
    col5: "",
    col6: ""
  ),
  a!gridLayout(
    headerCells: {
      a!gridLayoutHeaderCell(label: "Col1"),
      a!gridLayoutHeaderCell(label: "Col2"),
      a!gridLayoutHeaderCell(label: "Col3"),
      a!gridLayoutHeaderCell(label: "Col4"),
      a!gridLayoutHeaderCell(label: "Col5"),
      a!gridLayoutHeaderCell(label: "Col6")
    },
    addRowLink: a!dynamicLink(
      label: "Add",
      saveInto: a!save(
        local!gridData,
        append(
          local!gridData,
          a!map(
            col1: "",
            col2: "",
            col3: "",
            col4: "",
            col5: "",
            col6: ""
          )
        )
      )
    ),
    rows: a!forEach(
      items: local!gridData,
      expression: if(
        fv!index = count(local!gridData),
        a!gridRowLayout(
          contents: {
            a!textField(readOnly: true()),
            a!textField(readOnly: true()),
            a!textField(readOnly: true(), value: "Total"),
            a!textField(
              readOnly: true(),
              value: sum(index(local!gridData, "col4", {}))
            ),
            a!textField(
              readOnly: true(),
              value: sum(index(local!gridData, "col5", {}))
            ),
            a!textField(
              readOnly: true(),
              value: sum(index(local!gridData, "col6", {}))
            )
          }
        ),
        a!gridRowLayout(
          contents: {
            a!textField(
              value: fv!item.col1,
              saveInto: fv!item.col1
            ),
            a!textField(
              value: fv!item.col2,
              saveInto: fv!item.col2
            ),
            a!textField(
              value: fv!item.col3,
              saveInto: fv!item.col3
            ),
            a!textField(
              value: fv!item.col4,
              saveInto: fv!item.col4
            ),
            a!textField(
              value: fv!item.col5,
              saveInto: fv!item.col5
            ),
            a!textField(
              value: fv!item.col6,
              saveInto: fv!item.col6
            )
          }
        )
      )
    )
  )
)

thanks its worked

A suggestion, line 39: You can use fv!isLast instead of the condition. Also, adding a grid row layout outside should be less complex and easy to manage.